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It's not easy to view NTSC video input on a Windows box, but
thanks to Ask
MetaFilter I figured out how. Here's what you need:
Put it all together and your video is now showing on your screen,
where you can watch it, record it, filter it, etc. Some tweaking
improves quality. I found that it looked best if I ran
the capture at 640x480 and my display at 1280x960@60Hz. That's a nice
even 2x size multiple and (almost) the same refresh rate as the
source. Running at, say, 1024x768@85Hz introduced lots of ugly
interlace-related shimmer.
It's amazing how complicated this is. It's a lot of data: I'm
surprised my PC can record full motion video to hard drive. And the
NTSC input is in an awful format. The interlacing is the worst of it,
here's a nice visual explanation.
There's a neat program called DScaler that tries to deinterlace
the video before displaying. That gives a much sharper still picture but
in regions of high motion you get awful judder.
I gave up on it.
Progressive scan HDTV is the only rational thing.